Arizona city looks to Bluetooth to track traffic

Chandler uses a combination of Bluetooth detectors and ADOT freeway sensors to determine travel times that are posted on message boards

October 20, 2011

Chandler, Ariz., says that it is the first city in the U.S. to use Bluetooth to estimate traffic times on freeways, according to the East Valley Tribune.
The city uses Bluetooth detectors to track the movement of cell phones in passing vehicles. Data are also gathered from the Arizona Department of Transportation (ADOT)’s network of sensors on the freeway. A computer then adds the freeway and surface street travel time to display on message boards on the freeway. Each message board posts travel times to two points on the freeway.
“We update the travel times every minute so all of the information that you see on the signs are in real time, within one minute of being collected,” said city transportation engineer Mike Mah.
There is a limit to how much warning the message boards can offer, however.
Because the signs are only on the freeway, drivers about to enter the highway have no way of knowing if they can expect smooth sailing or gridlock.
Chandler has solved that problem at three of its busiest roads by posting actual travel times on digital message boards that are posted well ahead of freeway on-ramps. The signs are updated every minute, said Mah.
That gives drivers a chance to either accept a long commute—or to quickly plot another route.
“They know what the travel time is every day because they see it every day,” Mah said. “When the number changes, they’ll know that there is more or less congestion than what they typically see.”
The city has seven sensors mounted on poles that pick up signals from wireless devices. About 8 to 10% of passing vehicles have at least one Bluetooth device, Mah said.
The city developed the technology with Phoenix-based Oz Engineering. Oz has installed buried sensors in freeways that detect how fast cars are traveling. Those sensors would not provide valuable information on surface streets because they do not take into account how much time vehicles spend at red signals.
But tracking Bluetooth offers another challenge, said Tomas Guerra, an intelligent transportation systems manager at Oz.
Some mobile devices are in cars on the road, while other signals are coming from bicyclists, nearby homes or side roads. To calculate accurate travel times, a computer has to sort out what signals are likely on the road and which ones are not.
“Those are the things that make it more of an art than a science,” Guerra said.
Chandler has had the system in place since June, and the Intelligent Transportation Society of Arizona (ITS Arizona) has named it the best state project of the year.
The $400,000 cost was funded by a federal grant. Signs operate from 6 a.m. to 7 p.m. Monday through Saturday.
The Bluetooth detectors collect media access control addresses that are unique to each electronic device. That does not include a phone number or who owns the device, Mah said.